Towards reconciling national emission inventories with the globalbudget for methane

摘要

The global methane source to the atmosphere from human activities is determined only to within about 20%,and its evolution over recent decades is essentially undetermined.Current estimates of this global anthropogenic source are in the range 300–450 Tg yr?1 according tothe IPCC Assessment Reports.This estimate is based on a ‘top-down’ approach from the globalmethane cycle: atmospheric methane is removed at ~576 Tg yr?1 and accumulates at ~22 Tg yr ?11,implying a total source of ~598 Tg yr,?1 of which ~220 Tg yr ?1 is of natural origin.Approaching theanthropogenic source from a ‘bottom-up’ inventory (ie,by aggregating global source estimates)carries even greater uncertainty.While such an inventory could in principle be compiled fromemission inventories reported to the UN Framework Convention on Climate Change (UNFCCC),many inventories are unreported and most if not all the others have high uncertainty.Reconciliationbetween top-down and bottom-up approaches is attempted here as an approach towards budgetclosure,guided by carbon isotope information that constrains reconciliation.The ultimate goal is toreconstruct the decadal history of the global methane inventory.